Studies are underway to identify chemical neurotransmitters in photoreceptor cells and other retinal neurons, and to examine the role of chemical neurotransmitters in processing visual information. Particular attention is given to the role of biogenic amines in visual function. Two systems are currently being investigated: (1) the relatively simple visual system of Limulus polyphemus and (2) dissociated mammalian retinal neurons grown in monolayer culture. Biochemical (high voltage electrophoresis and high performance liquid chromatography coupled with electrochemical detection) and anatomical (autoradiography) techniques are employed to identify and localize chemical neurotransmitter systems present in these preparations. Electrophysiological techniques are being developed to study the interactions of isolated retinal neurons.